Switched-type chargers are widely used in the fields of smartphones, tablets, etc. due to its advantages of relatively small size, high efficiency, and fast charging speed. However, the output power and output current of a universal serial bus (USB) interface of an external power supply (e.g., an adapter, a computer, etc.) are usually limited. Generally, an external power supply may supply power for a switched-type charger during the battery charging process. The input current of the charger may be limited so as to avoid an overload condition when using an adapter or a USB power supply as a power source.